Ammonium nitrate (AN), with the chemical formula NH4NO3, is a worldwide available chemical compound, produced in millions of tons every year. Its main use is as a fertilizer, and therefore it is widely availability and easily accessible in many countries around the world. Its second main use is for the manufacture of explosives, and it is by definition very closely controlled.
An undesired use is for the production of home-made explosives (HME's) such as a mixture of ammonium nitrate and fuel oil (ANFO) or a mixture of ammonium nitrate and nitro methane (ANNM), of which the recipes are publicly available, for example on the Internet. In practice, to produce an HME out of AN-based fertilizer is rather straightforward, and misuse of AN-based fertilizer into explosives occurs frequently, especially in the context of terroristic attacks, but also by farmers for various blasting purposes, by children or students experimenting with explosives, for example in the production of (illegal) fireworks.
To limit its misuse, many countries have banned the use of pure AN as fertilizer by limiting the nitrogen content of AN-based fertilizer. A typical fertilizer formula is the so-called calcium ammonium nitrate (CAN), i.e. a mix of ammonium nitrate with a carbonaceous filler (limestone, dolomite) and with a maximum AN-content of 80 weight %. Such CAN fertilizer has moreover the advantage of being well-balanced regarding soil pH, avoiding the natural acidification due to the conversion of ammonium nitrogen into nitrate nitrogen to be assimilated by the plants.
Many other AN-based fertilizers exist, not only straight nitrogen (N) fertilizers (with different degrees of N dilution by a filler or containing secondary nutrients such as e.g. Sulphur), but also NPK (indifferently NPK, NP, NK) and especially high N-NPK fertilizers. All of them can be misused, but of course, the preferred choice for a potential misuse would logically be to opt for a fertilizer which is the most concentrated in ammonium nitrate i.e. a straight AN fertilizer or a CAN fertilizer. However, the invention is applicable to all AN-based fertilizers, as long as they contain ammonium nitrate.
There are basically two routes to convert a AN-based fertilizer such as a CAN fertilizer into AN suitable for home-made explosives: (i) a dry route, where the AN-based fertilizer such as a CAN fertilizer is simply crushed and later mixed with other compounds; and (ii) a wet route, wherein the fertilizer is first dissolved into water, allowing to filter out the insoluble components such as limestone or dolomite, thus to get a more concentrated ammonium nitrate product, after removal of water by evaporation, compared to the dry route. The wet route requires more process steps, but definitively allows obtaining a more powerful home-made explosive.
There is a need to limit the potential misuse of AN-based fertilizers, in particular a CAN fertilizer as a precursor for an explosive on the one hand, without hampering their legitimate use by farmers for food production on the other hand.